The present invention relates to fuel tank systems for small engines of the type employed for portable appliances such as portable power generating sets, garden tractors, lawn mowers and other such devices where the fuel tank is either mounted on the engine or closely adjacent thereto. Fuel tanks of this type are typically refueled by removing the filler cap and pouring fuel from a container having a pouring spout, or by pouring from a container and using a funnel.
Small engine fuel systems have recently been subjected to mandated requirements for fuel vapor emission control and it has been required to prevent vapor emission from the tank during operation and when the engine is not operating.
Heretofore small engine fuel systems have often employed a tank having an open vent in the filler cap for providing make-up air in the tank as fuel was withdrawn but which permitted escape of fuel vapor to the atmosphere.
In order to meet the requirement that a fuel tank for a small engine not emit fuel vapor, the filler cap must be sealed to prevent fuel vapor emission. If the filler cap is sealed then other provisions must be made for admitting make up air to the tank during engine operation. Furthermore, provisions must be made for overpressure relief. Thus, it has been desired to find a way or means of sealing a small engine fuel tank, yet provide for make-up air and over pressure relief and to do so in a cost-effective manner without requiring redesign or retooling of the tanks.